- All medium voltage equipment shall be earthed by two separate and distinct connections with earth In the case of high.
- And extra high voltage the neutral points shall be earthed by not Less than two separate and distinct connections with earth, each having its own electrode at the generating station or substation and may be earthed at any other point provided ‘no interference is caused by such earthing.
- If necessary, the neutral may be earthed through suitable impedance.
- In cases where direct earthing may prove harmful rather than provide safety (for example, high frequency and main. frequency coreless induction furnaces). Relaxation may be obtained from the competent authority.
- As far as possible, all earth connections shall be visible for inspection.
- No cut-out, link or switch other than a linked switch arranged to operate simultaneously on the
- Earthed or earthed neutral conductor and the live conductors shall be inserted on any supply System.
- This however does not include the case of a switch for use in controlling a generator or a transformer or a link for test purposes.
- Grounding is not likely to reduce the total magnitude of over-voltage produced by lighting or switching surges. It can, however, distribute the voltage between phases and reduce the possibility of excessive voltage stress on the phase-to-ground insulation of a particular phase.
- Plate electrodes shall be of the size at least 60 c m X 60 cm, Plates are generally of cut iron not less than 12 mm thick and preferably ribbed. The earth connection should be joined to the plate at not less than two separate points. Plate electrodes, when made of GI or steel, shall be not less than 63 mm in thickness.
- Plate electrodes of Cu shall be not less than 3.15 mm in thickness.
- Plate electrodes shall be buried ouch that ii. Top edge is at a depth not less than 15m from the surface of the ground. However, the depth at which plates are set should be such as to ensure that the surrounding soil is always damp.
- Pipes may be of cast iron of not less than 100mm diameter, 2.5 to 3 m long and 13 mm thick. Such pipes cannot be driven satisfactorily and may, therefore, be more expensive to install than plates for the same effective Area.
- Water pipes shall not be use as consumer earth electrodes.
- Under fault conditions, the earth electrode is raised to a potential with respect to the general mass of the earth that can be calculated from the prospective fault current and the earth resistance of the electrode. The results in the existence of voltage. In the soil around the electrode, that may be injurious to telephone and pilot cables, whose cores are substantially at earth potentional, owing to the voltage to which the sheaths of such cables are raised.
- The voltage gradient at the surface of the ground may also constitute a danger to life, especially where cattle are concerned. The former risk arises mainly in connection with large elect rode systems as at power stations and substation.
- Earth electrodes, other than the. Used for the earthing of the fence itself, should not be installed
- In proximity to a metal fence to avoid the possibility of the fence becoming live and thus. Dangerous at points remote from the substation.
- The materials used for making connections have to be compatible with the earth rod and the copper earthing conductor so that galvanic corrosion is minimized. In all cases, the connections have to be mechanically strong.
- The cross-sectional area of every protective conductor which does not form part of the supply cable or cable enclosure shall be in any case, not less than
a) 2.5 mm2, if mechanical protection is provided and
b) 4 mm2, if mechanical protection ii not provided.
- Joints of protective conductors shall be accessible for inspection and testing except m compound-filled or encapsulated joints.
- No switching device .hall is inserted in the protective conductor, but joints which can be disconnected for test purposes by use of a tool may be provided.
- An auxiliary earth electrode shall be provided electrically’ independent of all other earthed metal, for example, constructional metalwork, pipers, or metal-sheathed cables. This requirement i. considered to be fulfilled if the auxiliary earth electrode is installed at a specified distance from all other earthed metal (value of distance under consideration).
- The earthing conductor leading to the auxiliary earth electrode shall be isolated to avoid contact with the protective conductor or any of the parts connected thereto or extraneous conductive parts which are, or may be, in contact with them.
- In TN systems, for cables in fixed installations having a cross sectional area not less than 10 mm2 for copper and 16 mm2 for aluminum, a single conductor may serve both as protective conductor and neutral conductor, provided that the part of the installation concerned is not protected by a residual current-operated device.
- However, the minimum cross sectional area of a PEN conductor may be 4 mm2, provided that the cable is of a concentric type conforming to Indian Standards and that duplicate continuity connections exist at all joints and terminations in the run of the concentric conductors.
- When the source of energy is privately owned, there should be no metallic connection with the
- General public supply unless there has been consultation with the electricity authority concerned.
- It should be emphasized that an installation together with its source of energy may not consist entirely of one particular type of system. In such cases, each part of that installation may be required to be treated separately without detriment to other parts of the same installation.
- RCD’s Having Minimum Operating Currents Greater Than 30 mA – These devices are intended to give indirect shock risk protection.
- The neutral points of each separate electricity system which has to be earthed at the power station or substation.
- GI/Copper Plate Size: 500mmX500mmX10mm.
- Wood coal powder and salt are in same quantity.
- Size of GI Strip: 300mmX10mm
- Size of GI Pipe: 2.5” Diameter.
- Minimum 1Ω Resistance should be available at a distance of 15mt.
- IR value of Earth resistance is less than 10Ω.
- Earthing resistance of earthing rod is changed from 0.3Ω to 0…8Ωbetween summer to winter.
- Distance between two earthing pit is 2 X Length of earthing electrode.
- If ground resistance is less than plate earthing (if hard rock) than Pipe earthing shall be used.
- Resistance between two earthing pit is negligible.
- Earthing of lighting protection should not mix with power system earthing.
- Lighting protection earhing should be 10 time stronger than normal earthing (use copper bus strip instend of wire)
- Jointing of earthing strip shall be overlap of min 50mm and for earthing wire overlapping shall be min 40mm
Plate / Pipe Earthing:
Plate Earthing Electrode
- for copper shall be 600X600X3.1mm and
- For Hot dip GI shall be 600X600X6.3mm.
Pipe Earthing Electrode.
- Earthing electrode shall consist of a GI pipe (class B of approved make), not less than 40 mm dia. and 3 meters long. CL pipe electrode shall be cut tapered at the bottom and provided with holes of 12 mm dia. drilled at 75 mm interval up to 2.5 meters length from bottom. The electrode shall be buried vertically in the ground as far as practicable below permanent moisture level, but in any case not less than 3 meters below ground level. The electrode shall be in one piece and no joints shall be allowed in the electrode.
Size of Excavation:
- Size of 1 meter diameter and 3 meter length shall be excavated after depth of 3 meter the size of excavation shall be 900X300X900mm depth.
- Plate / Pipe Electrode shall be in vertical position.
- GI/PVC pipe for Watering shall be used of 40mm Diameter, length of 3 meter ( contain hole of 12mm Diameter in Zigzag manner starting from 15cm away from bottom to 2 meter height ).
- At bottom 150mm layer of Salt and charcoal power shall be installed than Plate shall be installed.
- Alternate layer of 150mm of Salt and charcoal power shall be used up to 2.5 meter.
- Min 120kg of charcoal power and 120kg of salt shall be used for each earthing pit.
- The plate \ pipe electrode, as far as practicable, shall be buried below permanent moisture level but in no case not less than 2.5 M below finished ground level.
IS: 5039 Distribution Pillars. (<1kV AC & 1.2KV DC)
- Distribution pillars are used by a number of distributing agencies to interconnect, terminate, control, protect and sectionalize distribution feeders.
- They are generally located on public footpaths abutting the building line or along the kerb line of footpaths.
- The distribution pillars covered by this standard are intended to incorporate HRC type fuses/links only and of current rating not exceeding 630 amperes.
- This standard covers distribution pillars for voltages not exceeding 1 000 V ac or 1 200 V dc, the current rating in each outgoing or incoming circuit not exceeding 630 A, for use on ac or dc systems, in outdoor conditions.
Rating of Individual Circuits:
- The rated current of the outgoing or incoming circuits shall be as follows: 160, 200, 250, 400 and 630 amperes.
- NOTE 1 — These ratings correspond to those of fuse-bases.
- NOTE 2 — All the incoming circuits of the same distribution pillar shall have the
- same current rating and similarly all the outgoing circuits of the same distribution pillar shall have the same current rating. Unless otherwise specified the sum of the rated current of the incoming circuits shall be fixed at the 2/3 of the sum of the current ratings of outgoing circuits, rounded up to the nearest higher value of the preferred current.
Rated Diversity Factor:
- The rated diversity factor of the distribution pillar having several incoming and outgoing circuits is the ratio of the maximum sum at any one time, of the assumed circuits of all the circuits involved, to the sum of the rated currents of all the circuits of the distribution pillar.
- NUMBER OF FUSE-WAYS DIVERSITY FACTOR
- 2 and 3 0.9
- 4 and 5 0.8
- 6 to 9 inclusive 0.7
- 10 and above 0.6
Enclosure:
- It shall be in all respect suitable for outdoor installations. It shall be made from a suitable material to withstand rough usage and weather. If fabricated out of MS sheets the thickness of the sheet shall be at least 3.15 mm in accordance with IS : 1730-1989.
Doors:
- Distribution pillars shall have a set of double hinged doors at the front. Similar doors shall be provided at the back also; if specified.
- The doors shall be so fitted as to provide the interior with maximum protection from atmospheric conditions. The hinges shall be of such construction that the doors can be swung open by not less than 150°.
- In addition the hinged design shall permit doors being completely removed when necessary. The base horizontal member shall be completely removable to facilitate cable jointing
Canopy:
- The top of the pillar shall be fitted with a sloping canopy design of which shall be such that rain water shall not accumulate on the top.
Aprons:
- If required, an apron (two if there are doors at the rear also) shall be provided below the door level of the pillar.
- They shall be easily removable. The apron shall be made from a suitable material to withstand rough usage. If made from sheet steel, the thickness of the sheet shall be at least 3.15 mm.
Pillar Lighting:
- A bayonet lamp holder complying with IS : 1258-1987, with a tumbler switch, competing with IS : 3854-1988†, a three pin plug and socket complying with IS : 1293-1988 with necessary fuses and wiring shall be provided inside the pillar.
- Unless otherwise agreed between the manufacturers and user, on TPN fuse boards, terminals for the neutral conductor shall allow the connection of aluminum conductors having a current carrying capacity:
- (a) equal to half the current carrying capacity of the phase conductor with a minimum of 25 mm2, if the size of the phase conductor exceeds 25 mm2; and
- (b) equal to the full current carrying capacity of the phase conductor if the size of the latter is less than or equal to 25 mm2.
Bus-bar
- Suitable barriers shall be provided between bus-bars.
Earthing
- The metal casing of the distribution pillar shall be provided with two separate earthing terminals and the framework shall be metallically connected with the casing.